A Simple Open-Circuit Fault Diagnosis Method for Grid-Tied T-Type Three-Level Inverters With Various Power Factors Based on Instantaneous Current Distortion

Different open-circuit (OC) faults for grid-tied T-type three-level inverters with various power factors may lead to similar current distortion characteristics, making it challenging to locate the faulty switch. This article proposes an OC fault diagnosis method applied to grid-tied T-type three-level inverters, which hierarchically diagnoses the group-level and device-level faults. Based on the current distortion similarity analysis with various power factors operation, the switches in one phase are divided into two groups. Subsequently, the group-level fault detection is implemented by locating the half-cycle where the zero-section phenomenon occurs. Moreover, the device-level fault location is realized by injecting the specific switching signals. Simulations and experiments are performed to verify the analysis of the current distortion. The result considering various conditions shows the proposed approach's correctness and robustness. The proposed method is effective in the power factor ranging from 0 lag to 0 lead. The OC fault can be located within 6 ms.